JPS5919443B2 - Manufacturing method of voltage nonlinear resistor - Google Patents

Description

Detailed Description of the Invention The present invention relates to a method for manufacturing a voltage non-linear resistor, in particular, the sintered body itself exhibits voltage non-linearity, the varistor voltage is low, the temperature characteristics are excellent, and the limiting voltage ratio is small. The present invention aims to provide a method for manufacturing a voltage nonlinear resistor that can be practically used for absorbing high-energy surges in low-voltage circuits, for example, for absorbing giant surges in electric circuits of automobiles.

In recent years, pollution regulations and safety regulations for automobiles have been strengthened.
Along with this trend, complex electronic devices such as electronic injection devices, seatbelt lock systems, and anti-kid systems that use a large number of semiconductor elements are being installed in automobiles.

However, the electrical circuits of automobiles include generators, motors,
A major problem is that there are inductive loads such as various relays and solenoids, and when a circuit is switched, many switching surges are generated from these inductive loads, which destroy the semiconductor elements in the various electronic devices mentioned above. It is becoming.

Among these surges, for small ones with energy of 10 joules or less, use a Zener diode or a small amount of B i 203 or CO2032Mn in ZnO.
A voltage non-linear resistor (varistor) which is fired with the addition of 02 or the like can be used sufficiently.

However, when the battery is removed from the circuit, the surge energy is 50 to 3
Conventional Zener diodes or metal oxide varistors could not handle the large diameter of 0.00 joules.

This is because a Zener diode is a diode consisting of a single pn junction, and in order to increase surge energy resistance, a uniform pn junction must be formed over a very wide area, for example, 80 cnf or more.

However, with current semiconductor technology, such large-area pn
It is difficult to make a joint and the manufacturing cost is high, making it uneconomical.

In the case of a conventional metal oxide varistor in which the sintered body itself exhibits voltage nonlinearity, for example, 1 mrrt per unit thickness.
The varistor voltage (vt mAimvt >) is relatively high.

In order to use this in a low-voltage circuit and have a surge energy withstand capacity of several hundred joules, it is necessary to make a sheet-like element that is extremely thin and has a large area, mainly due to heat capacity.

However, with current ceramic technology, it is extremely difficult to obtain such an element.

In particular, it has been almost impossible to manufacture brittle sintered bodies such as metal oxide varistors.

Varistors whose main component is ZnO are already well known, but the most commonly used one is ZnO.
Bi2O3, MnO2, Co2O3゜5b203 in nO
．． Add a small amount of metal oxides such as Cr2O3 and NiO,
This is an element obtained by firing in air at a temperature of 100°C to 1400°C.

Its microstructure consists of ZnO particles with a diameter of several tens of μm or ZnO particles containing impurities, and Bi2O particles with a thickness of 1 μm or less.
It has a structure surrounded by a layer of metal oxide such as No. 3.

The voltage nonlinearity of this varistor originates from the metal oxide layer, and the varistor voltage per layer is about 1.5V.

The circuit voltage for automobiles is 12 to 16 V DC, taking into account fluctuations in power supply voltage, so in order to use it in such a low voltage circuit for surge absorption, the varistor voltage must be approximately 16 V.
It must be of a certain degree.

For this purpose, approximately 10 metal oxide layers must be present in series between the electrodes.

On the other hand, since the size of ZnO particles is about 10 to 30 μm, if you try to make an element with 10 metal oxide layers in series, you will have to reduce the thickness of the element by 0.1 to 0.
．． It must be about 3 friends.

Moreover, if we try to suppress the temperature rise when 300 Joules of surge energy is applied to 50°C or less, considering the maximum operating temperature of 150°C and the thermal runaway starting temperature of approximately 200°C, the specific heat of the ZnO varistor ( Approximately 0.125ca
From the heat capacity determined by the specific gravity (5.4 g/cr?L), a volume of approximately 22 i is required.

Therefore, if the thickness of the element is set to 0.2 mm, a sheet-like element with a diameter of approximately 120 mm must be manufactured.

Moreover, as mentioned above, metal oxide varistors are
Since the structure is such that the particles are wrapped in a thin metal oxide layer and baked and hardened, the ZnO particles tend to fall off.

Therefore, such a sheet-like varistor cannot be manufactured by methods such as polishing.

That is, in order to meet such requirements, it is an essential condition to lower the varistor voltage (V1171A/mm) per dragon.

In response to such demands, attempts have been made to lower the pressure to V 1 mA/mm and to add new additives to grow ZnO particles during firing.

For example, Bi2O3, Co203, Mn
02, Ti 02 etc. added, ZnO with B
When i2O3, Co20Co203t, BeO, etc. are added, ZnO crystal grains can be grown considerably, and the varistor voltage (V1mA/mm2) per varistor can be reduced to 40V or lower.

However, in any case, adding 5b203, which has a remarkable effect on improving temperature characteristics and surge resistance, suppresses grain growth and reduces V1mA/rILm to 5b2.
The increase is more than twice that of when 03 was not added.

Therefore, it has been difficult to improve the temperature characteristics without increasing the varistor voltage.

In particular, when used as a surge absorbing element for an automobile, the temperature characteristics are one of the most important characteristics, since it is used under high temperatures due to the mounting position.

Moreover, BeO was also unfavorable from a safety and health standpoint.

In another attempt, a method was considered in which ZnO fine particles obtained by crushing a ZnO sintered body in advance were sprinkled with additives, molded, and fired to obtain an element with a low varistor voltage.

However, if the ZnO molded body is simply fired, the grain growth rate of the ZnO particles is slow and the grain size does not easily grow to 50 μm or more even if the ZnO molded body is fired at high temperature for a long time.

Therefore, even if the particles obtained by pulverizing the particles are coated with additives and fired, the result will be v1mA/1III! It was not possible to obtain a device with a voltage of 20 V or less.

Since the ZnO particles obtained by this method are fired at high temperatures, sintering progresses significantly, and the sintered bodies coated with additives, molded, and fired show almost no shrinkage. The device had extremely large numbers of pores and had moisture resistance problems.

In addition, since the contact between ZnO particles is close to a point contact state, the current density at the contact point increases during surge absorption, and the control voltage ratio at large current (for example, the voltage VIOA at IOA and varistor voltage v1m
(ratio to A) increases.

In addition, if a high-energy surge that generates heat is applied, there is a problem such as the heat generation at the contact point and the resulting melting, resulting in a significant deterioration of the characteristics.In particular, there is a problem such as absorption of giant surges that occur in automobile circuits. It was inappropriate.

The present invention solves the above problems and varistor voltage (V1
mA/mrIL) is low, there are few pores, and the limiting voltage ratio (
The present invention aims to provide a new manufacturing method for an overvoltage absorbing voltage nonlinear resistor with low VIOA/Vl mA), excellent temperature characteristics, and high energy surge resistance.

Its characteristics are that Zn(], Bi1 and Co
Alternatively, in a formulation in which Mn or CO and an oxide such as Mn are always added and the sintered body itself shows remarkable non-homogeneous properties when mixed, molded, and fired, a part of the ZnO raw material is
Bat Sr, Cat Na with nO as the main component
ZnO particles obtained by decomposing a sintered body containing 0.1 to 5 moles of at least one potash earth or alkali metal component in the form of an oxide with water. (core ZnO particles) and additive components other than Bi203r and C, which are not solid dissolved in the spinel phase, and a part of the ZnO raw material are mixed, molded, fired, and then powdered to create a spinel phase. The manufacturing method involves replacing the compound with powder, mixing it, molding it, and firing it.

The details will be explained below based on examples.

〔Example〕

0.5 mol of BaC for 99.5 mol of Zn
After adding O3 and mixing thoroughly, press molding and heat to 1400°.
C. for 10 hours.

The obtained sintered body has Z particles with a particle size of approximately 30 to 200 μm.
The structure is such that nO crystal particles are surrounded by a barium oxide layer several 100 layers thick.

This sintered body was boiled in pure water to dissolve the Ba component at the grain boundaries in the water, thereby breaking the sintered body and taking out the ZnO crystal particles in the sintered body as they were.

The obtained ZnO crystal particles have a particle size of approximately 30 to 200
It had a diameter of μm and consisted of about one or two single crystals.

Next (Zn0c′CBi shown in Table 1, Column I),
In a formulation that necessarily contains oxides such as Sb and Co or Mn or Co and Mn, mixing between a portion of the ZnO raw material and all additives other than components not solidly dissolved in the spinel phase (e.g. Bi2O3, 5iO2), Mold, 1
A spinel phase compound was produced by firing at 350°C for 2 hours.

Table 1, column (2) shows the composition of the spinel phase compound formed in the formulation in column (2).

These fired samples were pulverized to produce powder samples of spinel phase compounds.

Next, using the formulation number shown in column (■) of Table 1, large ZnO particles with a size of 63 to 125 μm were extracted from 10 moles of the ZnO raw material by the method described above, strained with O so as not to change the composition of the entire system. (core ZnO particles), and B
Additives other than 1203t 5102 and a portion of ZnO were replaced with a spinel phase compound powder sample having the composition shown in column (2) of Table 1, mixed, molded, and fired at 1300°C for 3 hours.

The sintered body thus obtained had a diameter of about 14 mm, and an ohmic electrode was provided thereto to measure its performance as a surge absorbing element.

The results are shown in the column a of Table 2-1°2.3, 4.

In addition, in the composition corresponding to 1-3 in column (■) of Table 1, this method (method a)/I shows that when the amount of substitution to the core ZnO particles is fixed at 10 mol and the firing conditions are changed. The characteristics are shown in Table 3, and the particle size of the core ZnO particles is 63 to 125.
Table 4 shows the characteristics when the thickness is changed from 44 to 105 μm.

[Comparative example]

The characteristic values obtained when a sintered body having the same composition as the example and the raw materials in column I of Table 1 were produced under the same conditions as the example are shown in Tables 2, 1 and 2. ,3,
It is shown in the C method column of 4.

In addition, the characteristic values when 10 moles of the ZnO raw material were replaced with core ZnO particles in the formulation shown in column 1 of Table 1 with the same composition as in the example are shown in b of Table 2 1, 2, 3゜4.
It is shown in the method column.

Next, using the formulation 1 in column I of Table 1, we replaced 10 moles of the ZnO raw material with core ZnO particles, and further changed the composition of the spinel phase compound to replace additives according to the formulation. , the composition of the spinel phase was kept constant, and the total amount of 5b203 in each formulation in column (■) was added by adjusting the amount of the spinel phase compound added and included in the spinel phase. The characteristic values obtained when the missing additive components were further added in an amount of G to give the same composition as in column I as a whole are shown in column d of Table 2.

In this case, the spinel phase compound is ZnO
6,98,5b203117, CO2030,44t
MnO,, 0,44t NiOO,s 9 tCr20
A material having a composition of 30.09 was used.

In Tables 2, 3, and 4, the surge breakdown energy is the energy applied to an element when the element is destroyed by a surge, expressed with respect to unit varistor voltage; for example, the surge breakdown energy is 1 joule. The element (J) becomes 1 when setting 1mA to 16V.
It means to destroy it with 6 joules of surge energy.

Therefore, it can be said that the larger the breakdown energy, the more suitable the material is for absorbing high energy in a low voltage circuit, which is the object of the present invention.

In addition, the temperature charge rate is 10
Voltage V1ol generated across the element when μA flows
It is the value obtained by dividing tA (150°C) by the voltage V1mA (RT) generated across the element when 1mA flows at room temperature.

This value is a guide to the quality of both the temperature characteristics and voltage nonlinearity characteristics of the varistor, and the larger this value is, the better these characteristics are. It is suitable for absorption and serves the purpose of the present invention.

As is clear from comparing methods D and C in Table 2, method D allows the core ZnO particles to have the effect of greatly reducing the varistor voltage V1mA/mm for any composition containing ZnO as the main component. show.

This is because the added core ZnO particles absorb fine ZnO particles and grow even larger, so that a sintered body with good sinterability is formed.

Generally, in zinc oxide varistors made by adding B i 203 and other additives to ZnO, the inclusion of 5b203 improves the temperature characteristics and surge resistance characteristics, but the solid phase reaction involving the sb acid component during the heating process This was a difficult point because it was not possible to lower the voltage because it was related to the phenomenon of suppressing grain growth.

However, when core ZnO particles are added, Zn due to the sb acid component
Since the grain growth rate of the core ZnO particles is greater than the grain growth suppressing effect of nO, a lower voltage can be achieved, and an element with significantly better temperature characteristics than a system not containing the sb acid component can be manufactured.

On the other hand, as shown in the d method column of Table 2, if a substance whose main component is a spinel phase containing an sb acid component is prepared in advance and added in place of 5b203, s
Since the solid solution spinel phase compound containing b is stable with respect to Bi2O3, it is possible to almost avoid the solid phase reaction involving the sb acid component, which is related to the grain growth suppressing effect of ZnO, during the heating process, and to that extent the nuclei are It has been found that the grain growth rate of ZnO particles increases.

Therefore, compared to when adding 5b203, the grain growth rate is higher, and the sinterability is significantly improved, with more uniformity and fewer pores, and the varistor voltage ("1 mA/ mm), reduced limiting voltage ratio (v1oA/v1mA), improved surge characteristics,
Further improvements in temperature characteristics have been made.

In addition to this, the yield of the product was significantly improved.

In this way, by using the d method, which is an improved version of the b method, it is possible to fabricate an element with characteristics that can be put to practical use.

In this case, by including the sb acid component in the spinel phase compound and adding it, the solid phase reaction involving the sb acid component can be controlled and the grain growth effect of ZnO can be suppressed.

However, in this method, the 5b203 component is not the only component, but other additive components that exhibit the effect of suppressing the grain growth of ZnO are added, so that the effect of suppressing the growth of ZnO grains by these components is exerted.

Therefore, if the effect of inhibiting the growth of ZnO grains due to these components can be suppressed, it is possible to achieve even lower pressure, and the particle size distribution of ZnO particles in the sintered body becomes uniform, which is desirable as it further improves the properties.

In the present invention, by solving this problem, the characteristics can be greatly improved.

That is, as shown in the example, Bi, ZnO,
Sb and C.

Alternatively, in a formulation in which Mn or Co and oxides such as Mn are always added and the sintered body itself exhibits remarkable non-ohmic properties when mixed, molded, and fired, part of the ZnO raw material is replaced with core ZnO.
When replacing the particles with additives other than Bi2O3 and Si02 and a part of ZnO with a spinel phase compound powder formed from them, mixing, molding, and firing, the result is as shown in Method a column of Table 2 1 to 4. In addition, it has become clear that it is possible to fabricate a device that can be made at low pressure and has excellent other characteristics.

This is due to the ability to control the ZnO particle growth suppression effect of additive components other than 5b203, which was achieved in the d method, by improving sintering properties such as improved uniformity and decreasing porosity, and by increasing the varistor voltage (V1mA/11mA). ) reduction, limiting voltage ratio (VIOA/V1mA), improvement of surge characteristics,
This is due to the fact that it has become possible to further improve temperature characteristics.

In addition to this, Tsuru as a product has significantly improved.

A number of advantages result from the significantly lower pressure achieved.

For example, Table 3 shows changes in characteristics when the firing conditions are changed in this method.

Since the degree of pressure reduction is large, it is fired at a lower temperature, and
By reducing the amount of i2O3 dissipated, temperature characteristics can be greatly improved and energy can be saved.

For example, as shown in Table 3, the temperature is 1300°C3 using the d method.
The properties obtained by firing for hours can be obtained by firing at 1200° C. for 3 hours, and the temperature characteristics can be greatly improved.

Table 4 also shows that in method a of the present invention, the firing conditions were fixed at 1300°C for 3 hours, and 10% of the ZnO raw material was
This figure shows the change in characteristics when the particle size range of the core ZnO particles to be substituted by molar ratio is shifted to the smaller side.

Since the effect of pressure reduction and homogenization in method a is large, uniformity can be improved by using smaller core ZnO particles, and the limiting voltage ratio and temperature characteristics can be significantly improved.

In the examples, core ZnO particles having a diameter of 63 to 125 μm or 44 to 105 μm are used, but there is no need to limit the particle size to this range.

For example, if there is no need to reduce v1mA/mm much, a particle in a smaller particle size range may be used, and if it is desired to significantly reduce v1mA/mm, a particle in a larger particle size range may be used.

By changing the particle size within the range of 30 to 200 μm, it is possible to easily produce a low-voltage element with any varistor voltage.

Regarding non-ohmic properties, in this method, components such as Co and Mn that contribute to improving non-ohmic properties diffuse from the spinel phase into other coexisting phases at high temperatures, so b, c, d, etc. Properties equivalent to those obtained can be obtained.

In the examples and comparative examples shown in Tables 2, 3, and 4, core ZnO particles made by adding B a COs to ZnO are used, but core ZnO particles can also be made of other materials. , Sr, Ca, Na, K in ZnO.

It can also be produced by a method in which a sintered body to which alkaline earth or alkali metal components such as Li and Cs are added is decomposed with water, and their core ZnO particles may be used.

In addition, although pure core ZnO particles are used in these examples, they do not necessarily have to be pure, and any component that can be solid-dissolved in ZnO without impairing the varistor action may be dissolved in the ZnO crystal in advance. You can leave it there.

B 1203 t S b2031 Co2O in ZnO
In a zinc oxide varistor doped with 32Mn02tNiOtCr20B, etc., Co2Mnt is present in the ZnO crystal phase.
The Nt acid component is dissolved in solid solution.

These components that can be solid-dissolved in ZnO are added to ZnO together with Ba component.
Even when nO is added and fired, a sintered body similar to that obtained when only Ba component is added is obtained, and by decomposing this with water, Zn(] and Co.

Core ZnO particles in which MntNi is dissolved can be taken out.

Even when these core ZnO particles are used in place of the pure core ZnO particles in the Examples and Comparative Examples shown in Tables 2 to 4, there is almost no difference in the characteristic O, and the characteristics tend to improve.

In the production of core ZnO particles, a method of boiling in pure water is used in the examples.

This is to increase the dissolution rate of the grain boundary layer in water, and the same effect can be obtained even if the grain boundary layer is left in water.

The purpose of boiling is to promote the decomposition of the sintered body, and is not an essential condition for taking out the core ZnO particles.

In addition, in the examples and comparative examples shown in Tables 2 to 4, the base formulation always contains oxides such as Zn(], Bi, Sb and Co, or Mn, or Co and Mn, and Cr, N
Although we use a formulation that contains oxides such as Cr t Nt t St, it is the same even if it contains ingredients other than oxides such as Cr t Nt t St that are effective in improving voltage nonlinearity characteristics and other varistor characteristics. Of course, it has the effect of

As explained above, the present invention provides ZnO with Bi2O3
When core ZnO particles are added to a formulation containing at least ZnO and fired, the core ZnO particles grow significantly.
Add at least Bi2O3 and 5b203 to
In a formulation containing oxides such as o, Mn, Ni, and Cr, adding it to the spinel phase compound of the sb acid component, which has a remarkable effect on improving temperature characteristics and surge resistance characteristics, can improve the grain growth of ZnO. It is possible to suppress the solid phase reaction involving the sb acid component, which is related to the suppression of sb.
The effect of inhibiting grain growth of ZnO due to the acid component is suppressed;
and that if all additives other than the sb component that are solid-dissolved in the spinel phase are added without being included in the spinel phase, the ZnO grain growth inhibiting effect of those additives will be suppressed;
etc. are used.

The present invention provides an element for absorbing high-energy surges in low-voltage circuits, which can be used not only at room temperature but also at 150°C and above.
It has now become possible to produce a voltage nonlinear resistor with a high yield that can be used in practice as an element that can be used even in a high temperature range of 200° C., for example, as an element for absorbing giant surges in automobiles.

Moreover, using the technology based on O of the present invention, Bi is added to ZnO.

In a formulation that always contains oxides such as sb and Co or Mn or Co and Mn, the amount and particle size of core ZnO particles to replace a part of the ZnO raw material, the particle size of the sb acid component spinel phase compound, the firing conditions of the element, etc. By changing the varistor voltage, a voltage nonlinear resistor with an arbitrarily low varistor voltage and excellent temperature characteristics and limiting voltage ratio characteristics can be easily manufactured.

Claims (1)

[Claims] In a formulation in which BttSb and oxides such as Co or Mn or Co and Mn are always added to ZnO, and when mixed, molded, and fired, the sintered body itself exhibits non-ohmic properties, 1 to 40 mol of the total Replace the ZnO raw material with ZnO particles with a particle size of 30 to 200 μm,
In addition, a powder of a spinel phase compound prepared by mixing, molding, firing, and pulverizing additives other than additives such as Bi that do not dissolve in the spinel phase and a part of the ZnO raw material. A method for manufacturing a voltage nonlinear resistor, which includes replacing the sample with a sample, mixing, molding, and firing.